This invention relates to materials handling equipment, and more particularly to apparatus for lifting and dumping detachable containers.
It has become a common practice to provide a number of detachable containers at various locations for receiving refuse. These containers are emptied periodically into the body of a truck, in which the refuse is compacted and then transported to a disposal area. The collection vehicle typically has an enclosed body with an opening at the top for receiving the material from the container. A pair of hoist arms are mounted for vertical swinging movement about a horizontal axis located behind the cab of the vehicle on the truck frame. The hoist arms each have a fork which is adapted to fit into sleeves on opposite sides of the container. The container has hinged cover doors at the top and when the hoist arms are raised, the container is picked up and transported over the cab and then inverted, causing the contents to fall from the container through the opening in the top of the body. The container is then returned to the ground by swinging the arms downwardly.
Usually, the forks are pivotally mounted on the hoist arms and the angular displacement of the forks relative to the hoist arms is controlled by hydraulic cylinders connected at one end with the hoist arms and at the opposite end with the forks. The fork cylinders are used primarily to tilt the container relative to the hoist arms as it is being raised to a dumping position. Examples of container dumping vehicles of this type are described in U.S. Pat. Nos. 2,951,600 and 3,078,000.
Conventional container hoist apparatus is controlled by manual hydraulic valves. One valve lever controls the raising and lowering of the hoist arms, another valve lever controls the angle of tilt between the forks and the hoist arms and a third valve lever controls movement of a packer head in the body for compacting the refuse after it has been dumped out of the containers. When the operator of the vehicle dumps a container into the body of the truck, it is necessary first to swing the arms downwardly until the forks are aligned with the sleeves on the container which is located directly in front of the vehicle. The vehicle is then moved forward to allow the forks to enter the sleeves in the container. At this time, the forks are approximately horizontal. The hoist arms are then raised toward the opening in the top of the body. As the arms swing vertically, the forks must be lowered gradually in order to maintain the container approximately horizontal, and thereby to avoid spilling the contents of the container. Typically this is done by opening the manual fork valve and using the weight of the container to swing the forks downwardly as the hoist arms are being raised. This requires careful coordination by the operator between movement of the arm valve lever and the fork valve lever. An inexperienced operator often has difficulty in coordinating these movements and will usually resort to a step-wise operation in which the arms are raised a few degrees and stopped, and then the forks are lowered a few degrees to compensate for the movement of the arms. These steps are then repeated until the container is over the hopper and ready for dumping. The lack of coordination between the movement of the forks and the arms does not allow the lifting portion of the operation to be performed at its optimum efficiency. Also, there is a danger that the fork valve lever will be moved in the wrong direction inadvertently, thereby spilling the contents of the container. Another problem with individual manual controls for the hoist arms and the forks is that additional time is required to train new operators to coordinate movement of these controls.
Various attempts have been made to provide automatic leveling of the forks while raising the hoist arms. It has been proposed, for example, to use limit switches and various cam devices for operating the fork cylinders in response to predetermined positions of the hoist arms. Another suggestion has been the use of a parallelogram linkage between the hoist arms and the forks. Neither of these proposals is satisfactory. The use of limit switches or other mechanical devices on the body of the truck requires accurately positioning the devices on the vehicle, but the vehicle is usually subjected to severe shock, leading to inaccuracies in the operation. Also, these systems require extensive wiring and are difficult to install on existing equipment. The parallelogram type loader has several moveable interconnecting links and the joints connecting these links are subject to wear and are a source of possible failure.